A carbon nanotube (CNT) is a very minute substance having an outer diameter of the order of nanometer and comprising cylindrical shape carbon hexagonal plane having a thickness of several atomic layers, which was found in 1991 (Non-patent Document 1). A carbon nanotube composed of a single layer graphene sheet is called a mono-layer CNT or SWCNT (Single-walled Carbon Nanotube) having an outer diameter of about 0.5 nm to about 10 nm, and a carbon nanotube composed of multi-layer graphene sheets is called a multi-layer CNT or MWCNT (Multi-walled Carbon Nanotube) having an outer diameter of about 10 nm to about 100 nm. Currently most of commercially available carbon nanotubes are multi-layer CNT, which are a mixture with carbon fibers and graphite fibers that do not form a tube.
A graphene layer consisting CNT can hold either of electron or hole as a carrier, and therefore, it can form any of intercalation compounds of electron-accepting acceptor type and electron-donating donor type. These intercalation compounds have been researched and developed so far in a graphite having many laminated graphene layers and are known as graphite intercalation compounds (Non-patent Document 2).
Production methods of a carbon nanotube are described in, for example, Patent Document 1 and Patent Document 2 and explained systematically as follows.
1) Arc discharging method
High voltage is applied between carbon electrodes in vacuo or under reduced pressure to cause arc discharging and deposit carbon vaporized at locally super high temperature (4050° C.) on the negative electrode.
2) Laser vaporization method
Laser is emitted to a mixture of carbon and a catalyst in vacuo or under reduced pressure to vaporize carbon at a locally super high temperature (4050° C.), and grow the vaporized carbon into CNT on the catalyst.
3) Chemical vapor deposition method (CVD method)
CNT is deposited on a catalyst by passing a carbon-containing gas (hydrocarbon) and a metal catalyst through a reaction tube heated to 1000-2000° C.
4) Other methods such as SiC surface decomposition method and polymer blend spinning method